Recover data iPhone

Restore your calendars and events on iCloud.com

1. If you do not have shared calendars, go to the next step. ... 
2. On iCloud.com, click. ... 
3. Click Restore Calendars. ... 
4. To the right of the version you want to restore, click Restore.

More items...

Restore your calendars and events on iCloud.com

Where are calendar events stored? Not on iCloud?

You have not mentioned where your calendar events are? Google, iCloud, AOL, Exchange, Outlook, Yahoo or any Other

Refer to the pic below, you may get your answer

Which is your default calendar? Settings > Calendar > Default Calendar

Settings > Calendar > Sync > [All Events] - Watch the GIF below